Tuning control system for high fidelity receivers



July 18, 1939.

G. L. BEERS TUNING CONTROL SYSTEM FOR HIGH FIDELITY RECEIVERS Filed June 27, 1956 flis /1 Blalp \SI/IFP 7'0 fiMPLIF/ER I 7'0 CONTROL GRIDS FOR Ill/7'0. 8E1. Co/v'rHoL INVENTOR George L. Beer-s Patented July 18, 1939 UNITED STATES PATENT OFFIQ TUNING CONTROL SYSTEM FOR, HIGH FIDELITY RECEIVERS of Delaware Application June 27, 1936, Serial No. 87,619

6 Claims.

The present invention relates to high fidelity radio receivers, and more particularly to a control system for adjusting the selectivity, when tuning, and for securing maximum fidelity when tuned.

It has for its object to provide means for simplifying the tuning operation in high fidelity receivers equipped with selectivity control means, such as is shown in my United States Patent No. 2,010,131.

Automatic selectivity control means may be included in the system whereby the receiver becomes automatically sharp in its tuning response to weak signals, and increasingly becomes broader in its tuning response in the presence of stronger signals.

In connection with manual means for limiting the broadening of the tuning in response to a received carrier wave, it is also an object of the invention to provide additional means for effect ing maximum selectivity when tuning, independently of the adjustment of said manual means.

It is also a further object of the invention to provide tuning control means adapted to secure maximum selectivity or a predetermined high degree of selectivity while tuning, and to permit automatically the broad or maximum fidelity adjustment to be assumed in the receiver upon completion of the tuning operation.

The invention will, however, be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

5 In the drawing, Fig. 1 is a schematic circuit diagram of a selectivity control system and tuning adjustment means for a high fidelity radio receiver embodying the invention, and

Fig. 2 is-a circuit diagram of a high fidelity 40 radio receiver provided with a modification of the system shown in Fig. 1, and embodying the invention.

Referring to Fig. 1, the tuning control elements of the receiver, such as a plurality of variable tuning capacitors 5, are connected with a common operating shaft indicated at 6, for gang operation, and are provided with a tuning control knob I having a shaft 8 and any suitable 50 mechanical means indicated by the dotted connection 9, whereby rotating of the knob causes tuning control movement of the capacitors. The shaft may be mounted on any suitable support 10 within the receiver and is provided with 55 means for operating a selectivity control switch in connection with the knob, which is located on a'panel or chassis element 4.

The switch and connecting means therefor, comprises a fixed collar II on one side of the support and a coiled compression spring [2 surrounding the shaft on the opposite side thereof.

The knob l is movable on the shaft axially between limits determined by the length of a slot l3 in which is located a pin [4 secured to and extending through the shaft. The spring l2 bears 10 against a leaf spring or contact member l5 which, in turn, contacts with the inner end of the knob I to move the latter outwardly with respect to the shaft, to the position shown in the drawing. It will .be seen that inward pressure on the knob serves to overcome the compression of the spring I2 and to permit the switch spring contact i5 to be moved inwardly, thereby to break contact with a fixed contact 5 and to make contact with a second fixed contact I1. 20

The contacts l5, l5 and H are arranged to change the selectivity, without changing the adjustment of the manual selectivity control device in the circuit, to substantially maximum selectivity, whereby the receiver may be tuned 25 more easily, exactly to a selected carrier wave by sound or by visual means. I

In my patent hereinbefore referred to, a control tube in connection with a potentiometer control device and circuits for controlling the selectivity of the receiver are shown and described, and in the present example, a similar control tube is indicated at l8. This is arranged to control the selectivity in a similar manner and for this purpose is provided with an output circuit l9 connected through a resistor 20 with an automatic volume control lead 2!, which extends to amplifier grids in the receiver as hereinafter shown, for automatic volume control thereof, and through a further resistor 22 with an 40 automatic selectivity control lead 23 extending to automatic selectivity control grids as' hereinafter shown, to apply automatic control potentials thereto. The application of control potentials from the control tube I8 is adjusted by a thereby to prevent the application of control potentials thereto.

The device 2425 provides manual selectivity or fidelity control by varying the ratio of the control potentials applied to the leads 2| and 23 from the tube l8, as the contact 24 is moved between the terminals of the control device 25. This results in maximum selectivity when the lead 23 is grounded, since the control grids connected therewith are grounded and the selectivity control means of whatever type provided is prevented from operating under control of the tube l8. An embodiment of this circuit in connection with a selectivity control tube will hereinafter be described.

The same result is obtained automatically in connection with tuning, regardless of the adjustment of the selectivity or fidelity control device 2425, by connecting the open contact I! through a lead 28 with the lead 23, whereby as the knob 1 is pressed inwardly in tuning, the lead 23 is grounded through the lead 28 and the con tacts l5 and H, which are then closed. The tuning adjustment of the capacitors 5 may then be effected under a condition of maximum selectivity to facilitate accurate tuning.

The circuit, as shown and described, represents any suitable control circuit for a high fidelity receiver of the type shown in the patent referred to, having manual means for adjusting the selectivity or fidelity. The specific embodiment herein shown and described has the advantage that the moving contact element is grounded, whereby the device is simplified in construction and may be applied to a receiver more readily and at lower cost.

Referring now to Fig. 2, the application of the system of Fig. 1 to a receiver of the superheterodyne type is shown, and in the circuit diagram, the same numerals are applied to the various circuit elements as found in Fig. 1. This system is essentially the same as shown in my patent above referred to.

The radio receiving system illustrated, includes a radio frequency amplifier 32, the input circuit 33 of which is tuned by one of the capacitor elements 5, and receives signal energy from an antenna circuit 34.

The radio frequency amplifier tube may be coupled to further amplifiers and a first detector, all of which have been omitted for the sake of simplifying the drawing, and the next tube shown in the signal channel of the receiver is the first I. F. amplifier tube indicated at 35, which is provided with a tuned input circuit 36 coupled to the detector output circuit 31, through a primary winding 38.

The grid 39 of the first intermediate frequency amplifier tube is connected through the lead 2| to the broad terminal 40 of the selectivity control potentiometer 25 which, in turn, is connected between the two control resistors 26 and 22, as in Fig. l. The lead I9 is connected to the output anode 4! of the control tube l8 and variable negative biasing potential is developed between the anode 4| and ground, as determined by the current flowing through the resistor 29. This current varies in accordance with the strength of a received signal in the same manner as in the system described in the aforementioned patent.

The resistor 29 is employed to maintain the impedance in the anode circuit substantially constant as the contact 24 is moved along the resistor 25. Anode potential is derived from a source represented by supply leads 43.

The intermediate frequency amplifier 35 is coupled to the second intermediate frequency amplifier tube indicated at 44 through an output lead 45 which is connected through the inductance 46 of the tuned input circuit 41 of the amplifier 44. The grid 48 of the amplifier 44 is coupled to the tuned circuit 41 through a coupling capacitor 49 and receives a biasing potential through a grid resistor 50 from a lead 5| which is connected to the automatic selectivity control lead 23 and the sharp terminal 52 of the selectivity control potentiometer 25.

The lead 23 is also connected with the control grid 53 of an auxiliary control tube 54, the cathode of which is connected to ground as indicated at 55, whereby the tube is biased by the potential existing on the lead 23, as derived from the control tube l8.

A relatively large voltage drop producing resistor 56 is provided in the output circuit of the tube 54 and across this resistor, through leads 5! and 58 are connected the control grid 59 and cathode 60, respectively, of an automatic selectivity control tube 61. The anode circuit 62 of the tube Si is connected through the inductance 46 of the tuned input circuit 41 of the second intermediate frequency amplifier 44 and serves to control the selectivity of the circuit in response to changes in grid potential derived from the tube 54 and the output resistor 56.

The radio frequency amplifier 32, the first intermediate frequency amplifier 35 and the second intermediate frequency amplifier 44 are provided with self bias resistors 68 to provide an initial bias potential on each of said tubes in addition to the bias potential supplied by the control circuit. It will be noted that as in the circuit of Fig. 1, the contact 24 is connected through the lead 26 to the contact 16 of the tuning control switch and, likewise, the contact I1 is connected through the lead 28 to the automatic selectivity control lead 23. The contact 15 is connected to ground at 21.

The second intermediate frequency amplifier 44 is connected to a second detector and automatic volume control means indicated at 65, and automatic volume control potential for the receiver is applied therefrom to the control tube 8 through an automatic volume control lead 66, whereby the current in the anode circuit of control tube l8 varies in accordance with signal strength, and thereby controls the tube circuits connected therewith.

In the present example, the biasing potential is supplied directly to the radio frequency amplifier 32 from the anode 4| through a bias potential supply lead 61, and since the resistance network 2&222529 in the anode circuit of tube I8 is connected between the anode 4| and ground, and the cathode of tube 32 is grounded through the self bias resistor 63, the bias potential is applied directly from the control tube l8 to the radio frequency amplifier 32.

The auxiliary control tube 54 receives its entire bias supply from the resistor network 20--2225 whereby when the contact 24 is in the sharp position at the terminal 52, the device 54 is substantially without bias and the potential drop through the resistor 56 is relatively high, thereby biasing the selectivity control tube 6| beyond cut off and since the plate impedance of the tube 6| is then very high the maximum selectivity of the input circuit 41 is obtained. Under this condition the bias of the second intermediate frequency amplifier 44 is controlled entirely by the potential in its self bias resistor and is not controlled by the automatic volume control means through the control tube Hi.

When the contact 24 is moved to the position for broad response at the terminal 40, the first intermediate frequency amplifier is placed directly under control of its self bias resistor and is cut ofi from the automatic volume control means and the selectivity control system is controlled by the tube I8 in response to signals to provide a broad tuning response and higher fidelity as the signal strength increases.

The arrangement is such that as the signal strength. increases, the biasing potential applied to the control lead 23 increases negatively and applies a volume control potential to the intermediate frequency amplifier 44 and, likewise, to the tube 54, resulting in a decrease in the potential across the resistor 56 and a reduction in the plate impedance of the automatic selectivity control tube 6 I, thereby decreasing the selectivity of the circuit 4'l In the present example, it will be seen that signals received on the antenna indicated at 34 are amplified through the receiver channel, comprising the RF amplifier tube 32, and the intermediate frequency amplifier, comprising the tubes 35 and 44, and are applied to the second detector and automatic Volume control means 65 from which they are applied to the usual audio frequency amplifier It and a loudspeaker H,

A tuning or other suitable indicating device 72 is provided in the system and is shown in the present example as connected to the second detector. As is well known, deflections of a tuning meter may be arranged to provide an indication of the tuning adjustment of the system, a maximum, or in some cases, minimum deflection indicating the resonance. point for the tuning element such as a tuning capacitor 5.

The control system shown and described may include further radio frequencmy and intermediate frequency amplifier tubes controllable by the master control tube l8, and may be applied to any system of this character wherein the selectivity is controllable by potentials applied to a control circuit such as the circuit 23, to provide a change in fidelity and selectivity in response to variations in signal strength, and automatic volume control means provided through a circuit such as represented by the circuit 2| to which other amplifier tubes than the one shown may be connected for simultaneous control.

The control arrangement for the automatic selectivity control tube 6| includes loading circuit 62 in connection with one or more of the amplifier stages, and is such that the frequency response or fidelity characteristic of the receiving system is broad or maximum when the contact 24 is moved to the terminal of the potentiometer device 25 designated'as Broad, while the response is sharp and the selectivity is maximum when the contact is moved in the opposite direction to the terminal designated as Sharp.

For tuning the system accurately, it is desirable that the tuning response be sharp, and the switch 15 is provided with the contact H, by means of which the grid of the auxiliary control tube 54 is connected directly to ground 21 when the switch arm 15 is moved from the contact 16 to the contact 11, thereby immediately establishing a condition of sharp response or maximum selectivity, regardless of the adjustment of the contact 24, whereby the tuning means 5 may be adjusted for resonance most advanta eously. The broad or manually selected con,- dition of response is obtained by releasing the knob 1 and permitting the arm 15 to engage the contact 15 as hereinbefore described.

The switch may be actuated by the tuning control connection as described in the preceding figure and as indicated by the dotted connection l3-i3 between the tuning capacitor 5 and the control knob I. A pair of switch contacts 14 and 15 may be connected also with the control knob l to be closed when the switch arm I5 is moved to the contact 11, to cut on" the signal output as by short-circuiting the audio frequency channel, indicated in the present example by the connection 16. This modification by short circuiting the audio frequency channel when the contacts 'i4'l5 close, provides silent tuning with maximum selectivity, whereby a. carrier-wave may be tuned more accurately without disturbing noise. In this case, the tuning meter is used for obtaining a resonance adjustment.

I claim:

1. In a radio receiver having gain and selectivity control circuits, the combination therewith, of an automatic volume control system including an electric discharge control tube having an anode output circuit, a potentiometer device having its terminals connected with said output circuit and with said gain and selectivity control circuits for said receiver, said circuits having ground return means, a movable contact for said potentiometer device connected to said ground return means, and tuning control means providing a direct ground connection for one of said control circuits to the exclusion of said potentiometer contact.

2. In a radio receiver, the combination of manually operable tuning control means, a selectivity and fidelity control network including a circuit providing connections therewith for securing maximum selectivity and alternatively a manually adjusted predetermined degree of fidelity, means controllable by said tuning control means for selecting said first named connection whereby the tuning operation of the receiver may be made selective, and for effecting the other of said connections to restore the predetermined degree of fidelity when a tuned-in condition has been obtained.

3. In a radio receiving system, the combination of manually operable tuning control means including a tuning control knob rotatable to change the tuning adjustment of said receiving system and being movable axially, a grounded contact plate movable in response to axial movement of the control knob to effect a switching operation, means providing a pair of insulated contacts between which said contact plate moves in said switching operation, a selectivity control network in said system having an operating circuit connected with one of said last-named contacts, and an operating circuit for said network for securing maximum selectivity connected with another of said contacts, whereby the tuning op eration of said receiver may be made selective by axial movement of said control knob when tuning.

4. In a radio receiving system, the combination of manually operable tuning control means including a tuning control knob rotatable to change the tuning adjustment of said receiving system and being movable axially, a grounded contact plate movable in response to axial movement of the control knob to effect a switching operation, means providing a pair of insulated contacts between which said contact plate moves in said switching operation, and a selectivity control network for said system including a control circuit providing an adjusted degree of selectivity and a control circuit providing substantially maximum selectivity, each connected between ground and one of said insulated contacts, whereby said connections are controllable by axial movement of said tuning control knob for changing the response characteristic of the recciver for substantially maximum selectivity during the tuning operation and for restoring said receiver to a predetermined condition of adjustment of selectivity and fidelity upon completion of the tuning operation.

5. The combination with a high fidelity radio receiving system including means for adjusting the selectivity and fidelity thereof, said last named means including a potentiometer resistor and a selectivity control network in which said resistor is connected, a selectivity control circuit connected with one terminal of said resistor, a switch contact connected therewith, a second switch contact, means providing an adjustable connection on said potentiometer resistor for said second switch contact, means providing a ground connection for said contacts movable therebetween from the second named contact to the first named contact, and means for effecting said switching connection during a tuning operation of said receiving system.

6. In a radio receiving system, the combination with tuning control means, of a movable tuning control member therefor, a selectivity and fidelity control network for said receiving system having a circuit control element therein manually adjustable between limits providing maximum selectivity and maximum fidelity, switch means arranged to be actuated by said tuning control member for controlling a connection with said network whereby said control element is rendered inoperative, and means providing a connection with said network for eifecting maxi- 20 mum selectivity when said switch is actuated.

GEORGE L. BEERS. 

